Bo1 t B e r a n e k a n d N e w a n I n c o r p o r a t e d
C a m b r i d g e , M a s s a c h u s e t t si HAMPTON, VA. /MARCH [24][25][26]1975 Downloaded by UNIVERSITY OF TENNESSEE on September 29, 2015 | http://arc.aiaa.org |
sensorresponds twice as much to radial strain as to axial strain. For a fiber optic-or polymeric-type hydrophone, the strain sensor could be wound helically at 54.7 ø from the axial direction to obtain a truevolume response. Other winding methods will achieve similar acoustic results, but they will reduce the ability of the sensor to bend. Sensitivity of several designs will be discussed. 8:45 SS2. Design of rubber mandrel fiber optic hydrophones.
Facilities at AARC include an acoustic wind tunnel (AWT), a pressurized pulse tube, and a reverberant water tank. The AWT may also be used as an anechoic room. The AWT was designed primarily for the acoustic evaluation of submersible propulsors. It is large enough to use prototype hardware for an important class of such vehicles. A model afterbody with control surfaces and propulsor is submerged in an open jet surrounded by a large anechoic room. In addition to the low background noise levels and turbulence required for this duty, the AWT has a unique nose-sting model mounting arrangement that avoids the noise and flow disturbances of strut or wire supports. The pulse tube provides measurements of reflection and transmission properties of materials and coating systems samples at submergence pressures to 1000 psi and with controllable temperature. The acoustic water tank provides a highly reverberant facility useful for measurement of radiated power from submerged sources and has been used to measure radiation transfer gains by the application of reciprocity.
The acoustic sensitivity of an optical fiber consists of optical path length shifts resulting from pressure-induced density-mediated variations in index of refraction and from actual path length changes (strains) due to acoustically-induced stress. For free fibers these effects tend to cancel, thereby limiting sensitivity. By wrapping a fiber on a mandrel of a material with dynamic modulus smaller than that of the glass fiber, the pressure-induced strain in the fiber becomes governed by the response of the more compliant mandrel and the acoustic sensitivity of the resulting sensor can be significantly greater than that of a simple fiber. Models for acoustical (signal) sensitivity, response to noise environments typical of sonar spaces, and vibration sensitivity—all as functions of frequency—have been developed. These models include effects of the dynamic properties of the constituent materials, the dimensions of the mandrels, the angle of the wrap, etc. Analytical estimates for preliminary sensor designs and certain confirming laboratory measurements indicate that such sensors may perform as well or better than conventional hydrophones.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.